4. Direct and Indirect Retainers Flashcards
Direct Retainer
The component of a PRDP used to retain and prevent ____ consisting of a clasp assembly or attachment
dislodgement
Intracoronal - attachment placed into a crown NOT on the outside; often incorporated into provisional bridges & are nice bc they don’t show clasps.
2 Systems- indicative of how tight attachment
connects to crown:
\_\_\_\_ - fits v tightly / not loose; designed NOT to release stress. KC3 - bc it’s entirely supported by abutment teeth
____ - these
attachments “give” more Sometimes made w a ring + nylon (e.g. for
overdentures, we want
these prosths to be
supported/retained by the attachment BUT don’t
want it to torque the
abutment tooth.)
precision
semiprecision
Extracoronal - attachment is on outside of the crown (e.g. a ring soldered to the ____ aspect of a crown w an attachment that fits into it)
Retentive class assembly - most \_\_\_\_; fits around the tooth; 2 types indicating where bulk of clasp is located:
\_\_\_\_ (clasp is above height of contour except the retentive tip, which flexes over to engage) \_\_\_\_ (below HOC)
distal
common
suprabulge
infrabulge
Clasp Assembly
The part of a PRDP that acts as a ____ for a prosthesis by ____ encompassing or contacting an abutment tooth
direct retainer
partially
Terminology
Suprabulge
the surface of a tooth that is occlusal of the ____
Infrabulge
the surface of a tooth that is ____ of the height of contour
height of contour
gingival
Types of Clasp Assemblies
Suprabulge
____ or circumferential
Approaches ____ from the occlusal (____ height of contour)
Infrabulge
____ or bar
Approaches undercut from the ____ (____ height of contour)
Aker’s
undercut
above
roach
gingival
below
Clasp
That component of a clasp assembly that engages a portion of the tooth surface and either engages an undercut or remains above height of contour
Composition
Cast ____
Wrought wire
Configuration \_\_\_\_ Bar Combination Circumferential and bar Cast clasp arm and wrought wire clasp
Primary function
____
Bracing (____)
Directional approach to
the undercut
____
Infrabulge
metal circumferential retention stabilizing suprabulge
Retention
Resistance to ____ dislodging forces
Provided by the retentive clasp arm
Divided into three parts:
Proximal 1/3 (shoulder)- must be ____ and located ____ the survey line
Middle 1/3- must be ____ and ____ the survey line
Terminal 1/3- must be ____ and engage retentive ____ on tooth ____ the height of contour
vertical rigid above ridgid traverses flexible undercut below
Retention
Should be the ____ necessary to resist dislodging forces
Retentive areas on ____ side of the arch should be opposed by retentive areas similarly placed on the ____ side of the arch
minimum
one
other
Retention
To be retentive, the terminal end of the retentive clasp must be engaged in ____ area
Counteract dislodging forces that unseat the PRDP at ____ angles to the occlusal plane during function
undercut
right
Retention
Amount of retention depends on: 1. \_\_\_\_ 2. Flexibility of the clasp arm 3. \_\_\_\_ of the undercut 4. Length - – amount of clasp arm extending \_\_\_\_ the height of contour 5. \_\_\_\_
material
degree
below
shape
Flexibility of a Clasp Arm
Influenced by:
The cross-sectional form
____ clasp has greater flexibility than half round clasp with the same diameter
Diameter (cross-sectional size)
The smaller the diameter of the clasp, the greater the ____
round
flexibility
Flexibility of a Clasp Arm
Influenced by:
Length of the clasp
the longer the clasp, the greater the ____
The taper of the clasp
The more the taper, the more the ____
A ____ taper in both thickness and width is necessary
Clasp terminal should be ____ as thick as origin
flexibility
flexibility
uniform
half
Flexibility of a Clasp Arm Influenced by: The material (metal alloy used) Flexibility of the retentive clasp arm varies with different alloys used \_\_\_\_ \_\_\_\_
cast metal
wrought metal
Wrought Metal Clasps
Their longitudinal structure allow for greater degree of ____ than the grain structure of cast metal clasp
Are placed in slightly ____ undercuts (____ inch) than are cast clasps
flexing
greater
0.02
Wrought Metal Clasps Applied by: Soldering it to the \_\_\_\_ connector Soldering it to the \_\_\_\_
minor
meshwork
The B-L depth of retentive undercut and therefore, the position of the terminus of a retentive clasp arm is determined using undercut gauges in a dental surveyor
0.01” undercut: ____ metal clasp
0.02” undercut: ____ clasp
0.03” undercut: ____ used
cast chrome
wrought wire
rarely
Support
Resistance to ____ seating forces (displacement of the clasp assembly in a gingival direction)
Provided by the ____
Prevents ____ to periodontal structures
vertical
rests
trauma
Stability (Bracing) Resistance to \_\_\_\_ components of masticatory force Provided by \_\_\_\_ portions of clasps Other rigid components which contact vertical tooth surfaces Proximal Facial Lingual
Note: Retentive clasp ____ does NOT contribute to ____
horizontal
rigid
terminus
stability
Reciprocation
Resistance to ____ forces exerted on a tooth by an active clasp during ____ and unseating of the prosthesis
Each retentive clasp arm must be opposed by a ____ arm
horizontal
seating and unseating
reciprocal
Reciprocation
Positioned on the ____ side of the tooth from the retentive arm
Should always contact tooth ____ the retentive clasp arm when the clasp is being ____ on the tooth
opposite
before
seated
Adequate Encirclement
Each clasp assembly must engage a minimum of ____° of circumference of abutment tooth to prevent tooth from moving out of contact with clasp assembly
May engage ____ than 180°
180
more
Adequate Encirclement
Prevent ____ tooth movement from within the confines of a clasp assembly
May incorporate a minimum of ____ widely separated points of contact
horizontal
three
Passivity
A clasp assembly in place should be completely ____ (no active force on tooth)
Only when a ____ force (e.g. force in occlusal direction) is applied to the PRDP is the ____ function activated
passive
dislodging
retentive
Requirements of a Clasp Assembly
Retention- ____ necessary
Support- proper ____
Stability (bracing)- ____ portions of clasps and minor connectors
Reciprocation- ____ clasp arm
Encirclement- ____° or more to prevent tooth
movement
Passivity- no ____ force by clasp in place
minimum rests rigid reciprocal 180 active
Commonly used Clasp Assemblies for Tooth- supported PRDP \_\_\_\_ clasp assembly (Akers) Embrasure clasp assembly Cast circumferential and cast bar clasp assembly \_\_\_\_ clasp Modified T bar \_\_\_\_ bar I bar
circumferential
T bar
Y
Cast Circumferential Clasp Assembly
Excellent support, bracing and retentive qualities
Encircles tooth ____ than 180°
More frequently on teeth ____ to modification spaces
usable undercut on the abutment tooth is located on the side of the tooth ____ from the edentulous area
more
adjacent
away
Cast Circumferential Clasp Assembly
Retentive clasp arm
originates ____ height
of contour
terminal 1/3 is positioned ____ (engages undercut)
Reciprocating clasp arm
slightly ____ than the retentive clasp to promote rigidity
above
below
thicker
Additional Considerations for the Cast Circumferential Clasp
The ____ of the retentive clasp and the entire ____ of the bracing clasp should be located at the junction of the ____ 1/3 of the tooth occlusogingivally
proximal 2/3
length
middle and gingival
Proper Position of Retentive Clasp Terminus
Should not contact the ____
Should be located at the ____ portion of the gingival 1/3 of the tooth occlusogingivally
free gingival margin
gingival
Embrasure Clasp
Two ____ clasp assemblies originating from a common ____ connector
Indicated on side of arch where there is no ____ space
Must cross the marginal ridges of ____ teeth
circumferential
minor
edentulous
two
Embrasure Clasp
Occlusal rests on ____ teeth
Two cast ____ clasps
Two cast ____
clasps
Must provide sufficient space for adequate thickness of metal
Prepare rest seats and marginal ridges adequately
both
retentive
reciprocating
Bar Clasps
• Classified by shape of the ____
T bar, modified T bar,Y bar
• T and Y bar clasp arms are the most ____
• Only ____ of clasp is needed to be placed in undercut area
retentive terminal
misused
terminal
Bar Clasps
• In many cases the ____ portion of T or Y clasp arm may be removed because they are ____ the survey line and they become ____ T or Y bar clasp.
suprabulge
above
modified
Bar Clasp
Approach undercut from a ____ direction
More ____ than a circumferential clasp
gingival
esthetic
Bar Clasp
T bar
____ undercut
Modified T bar
____ finger omitted (____)
DB
nonretentive
esthetics
Bar Clasp
Y bar
____ are high on M & D but low on ____ of abutment tooth
I bar
on ____ of canines for esthetics
height of contours
center
DB
Here’s the T-bar in the ____ 1/3 picking up the undercut at 2 termini. This has been relieved (points in this green highlighted space); this is the approach arm. We don’t want this too high on the tooth.
gingival
Relationship of Bar Clasp to the Gingiva
• The approach arm must not impinge on the ____ adjacent to the abutment
• The approach arm should cross ____ to the free gingival margin
soft tissues
perpendicular
Contraindication to Bar Clasp • The clasp should not be located over a deep tissue \_\_\_\_ • A great deal of relief required may form a \_\_\_\_ interfere with patient comfort cause \_\_\_\_ to the mucosa of the lip or cheek
undercut
food trap
injury
Additional Design Considerations for the Bar Clasp
• The minor connector that attaches the occlusal rest to the framework should
be ____
contribute to the overall ____ and stabilization of the prosthesis
rigid
bracing
Commonly used Clasp Assemblies for Extension Base PRDP
____ clasp assembly
____ (RPC) clasp assembly
____ and wrought wire circumferential clasp assembly (combination clasp)
RPI
RPA
cast circumferential
RPI Clasp Assembly/
RPA (RPC) Clasp Assembly
RPI:
Rest (____)
Proximal plate (____)
Cast ____ bar retentive clasp engaging ____ or mid-buccal ____
Proximal plate and minor connector provide ____
MO D I 0.01" MB undercut reciprocation
Mechanics of the RPI Clasp Assembly
• Forces are transmitted through the PRDP components to the ____ rest directing mesial torquing and axial forces to the tooth
• Occlusal force causes rotation in the area of ____ rest
• I bar clasp arm and proximal plate ____ from the tooth during function
and move in a ____ direction
• The abutment tooth is braced mesially by an ____ tooth
mesial mesial disengage mesiogingival adjacent
Contraindication for the RPI Clasp Assembly
• No tooth undercut
• Severe tissue undercut
Clasp arm -no more than ____ mm from the soft tissue
Excessive relief may form food trap food, interfere with patient comfort or irritate the lip or cheek
• ____ buccal or labial vestibule
I bar arm should not interfere
with movable tissue
Superior border of the arm located at least ____mm from the gingival margin
2
shallow
3
Advantages of the RPI Clasp Assembly
Proximal plate and I bar move ____ from the tooth during function to reduce torque
Mesial minor connector and proximal plate provide ____ and eliminate need for a ____ arm (no need for lingual recontouring)
I bar is more ____
Mesial rest eliminates class ____ lever
away reciprocation lingual esthetic I
RPI Clasp Assembly/
RPA (RPC) Clasp Assembly
RPA Clasp Assembly:
Rest (____)
Proximal plate (____)
____ retentive clasp engaging ____ or mid-buccal undercut
Proximal plate and minor connector provide ____
Used where RPI clasp is contraindicated
severe tissue ____
____ B vestibular depth
MO D akers 0.01" MB reciprocation undercut insufficient
Assembly and Mechanics of RPA Clasp
- Forces are transmitted through RPD components to the ____ rest directing mesial torquing and axial forces to the tooth.
- Rotation occurs in the area of ____ rest.
- Circumferential clasp and proximal plate ____ from tooth during function.
- The abutment tooth is usually braced by a mesial ____ tooth.
mesial
mesial
disengage
adjacent
Combination Clasp
____ circumferential (reciprocal) clasp arm
A ____ circumferential (retentive) clasp arm
Indications
on an abutment tooth adjacent to a distal extension space when the usable undercut is on the ____ surface
greater ____ of retentive arm is desired
____ an advantage
cast wrought wire MB flexibility adjustability
Combination Clasp
Advantages:
may be used when a ____ projection clasp is contraindicated because of a soft tissue ____ below the tooth
can be placed in a ____ undercut area (____”)
____ occlusal rest, distal proximal plate
vertical undercut deeper 0.02 distal
Mechanics of Cast Circumferential and Wrought Wire Clasp (Combination Clasp)
Strategy – Reduce the effective Class ____ lever in distal extension partial by using ____ component in the resistance arm.
• Consists of cast, reciprocal arm and tapered, round wire, retentive clasp arm
• The retentive clasp is either ____ to a cast framework
I
flexible
cast or soldered
Mechanics of Combination Clasps
• Rotation occurs at area where minor connector breaks ____ with tooth
• Wrought wire retentive clasp tip moves ____ during function and directs a ____ torquing force on tooth
• Magnitude of the torquing force is influenced by the ____ of the wrought wire clasp
contact
occlusally
distal
flexibility
Advantages of Combination Clasps
• Flexibility- used when maximum flexibility required
Abutment tooth adjacent to ____ extension base.
Weak abutment, when a ____ type retainer contraindicated.
- Adjustability- when precise retentive requirements ____ and later on adjustment needed for retention.
- Esthetics – less bulkier than cast clasp. Wrought wire small diameter thickness, stronger because ____ in structure. Light reflected in such a way that the appearance of metal less obvious.
- Minimum tooth surface coverage – less ____ buildup
distal bar unpredictable round plaque
Disadvantages of Combination Clasps Involves extra \_\_\_\_ in fabrication Can be \_\_\_\_ by careless handling won’t \_\_\_\_ tooth It may distort with function and not engage tooth
step
distorted
stabilize
Ring Clasp
Most often indicated on ____ molars
____ almost the entire tooth from its point of origin
Entire clasp except for the ____ must be placed above the height of contour
An ____ arm is needed to prevent excessive f lexing
tilted/tipped
encircles
retentive tip
auxiliary bracing
Factors Determining the Selection of Clasp Assembly
A. Distribution of Forces
____ of forces to muco-osseous and dento- alveolar segments is required
____ clasps minimize lateral torquing forces directed to abutment teeth
____ clasps direct lateral torquing forces to the abutment teeth
distribution
stress releasing
non-stress directing
Factors Determining the Selection of Clasp Assembly
A. Distribution of Forces
Commonly Used Non-stress Directing Clasp
____ (circumferential) clasp
____ clasp
Commonly Used Stress Releasing Clasp Assemblies
____ (Rest, Proximal Plate, I-Bar)
____ (Rest, Proximal Plate, Akers)
Cast circumferential and wrought wire circumferential (____) clasp
akers
embrasure
RPI
RPA
combination
Factors Determining the Selection of Clasp Assembly
B. Location of Undercut
on ____ tooth will influence choice of retentive clasp arm
C. Minimal tooth and minimal gingival coverage
Clasps which ____ these tissues are preferred
Reduce plaque accumulation
D. Esthetics Influenced by visibility of clasp Bar clasps • confined to \_\_\_\_ 1/3 of tooth and contact less tooth surface area • approach undercut from \_\_\_\_ direction • are less conspicuous than \_\_\_\_ clasp
E. Clasps on Previous Removable Partial Denture
May indicate esthetic awareness and demand of patient
May indicate amount of ____ necessary
abutment minimize gingival gingival circumferential retention
Indirect Retainer
“The component of a removable partial denture that assists the direct retainer (s) in preventing ____ of the distal extension denture base by functioning through ____ action on the opposite side of the fulcrum line when the denture base moves ____ from the tissues in pure ____ around the fulcrum line” (GPT, 1999)
displacement
lever
away
rotation
Indirect Retainer
Should be positioned on the ____ side of the fulcrum line (center of rotation)
At ____ angles to and as far from the fulcrum line as possible
opposite
right
Indirect Retainer Forces causing vertical movement of the denture base away from the supporting ridge: pull of \_\_\_\_ foods forces created by \_\_\_\_ action \_\_\_\_
sticky
muscle
gravity
Indirect Retention \_\_\_\_ premolar an ideal location for an indirect retainer (no opposing maxillary cusp that occludes into this fossa) Anterior to \_\_\_\_ line (F) Resists lifting of denture base
mesial fossa of mandibular first
fulcrum
Indirect Retention
Without an indirect retainer, the PRDP may ____
dislodge
Types of Indirect Retainers
____
____ connectors and proximal plates
Others
____
Need rest seats prepared
Kennedy bar ____ connector
rests
minor
lingual plate
major
